1. Field of the Invention
The present invention relates to a large-sized projection screen, a lens sheet that is suitably used therein, and a base plate that is used in that lens sheet.
2. Description of the Related Art
As illustrated in FIG. 1, a lens sheet 1 has hitherto been being manufactured through the following processes. Namely, a temperature adjustment process (A) for adjusting the temperature of a mold 2 of the lens sheet 1 to the temperature that is suitable for molding the lens. The first resin coating process (B) for coating a liquid state of ionizing radiation curable type resin (hereinafter referred to as xe2x80x9cthe UV-curable resin) 3 to the entire surface of the temperature-adjusted mold 2. The second resin coating process (C) for coating the liquid UV-curable resin 3 to the portion on the pressurization starting side that is located on the mold 2. The base plate supply process (D) for applying the base plate 4, which permits the transmission of ionizing radiation through itself, to the mold 2 from above the UV-curable resin 3. The lamination process (E) for pressing the base plate 4 by means of pressurizing rolls 5a, 5b from the pressurization starting end side to a pressurization termination end side to thereby laminate the base plate 4 onto the UV-curable resin 3. The resin-curing process (F) for radiating the ionizing radiation onto the UV-curable resin 3 from above the base plate 4 to thereby cure it. The mold-release process (G) for exfoliating the thus-cured UV-curable resin 3 from the mold 2 jointly with the base plate 4.
The base plate supply process (D) is the one that is intended to cover the base member 4 of the lens sheet 1 to the mold 2 from above the UV-curable resin 3. For example, the sheet-like base plate 4 is adsorbed by a plurality of suckers that are disposed on a flat plane and is conveyed onto the mold 2 having had coated thereon the UV-curable resin 3. The suckers release the base plate 4 at a position above the mold 2, whereby the base plate 4 falls upon the coated layer of the UV-curable resin 3 and is adhered onto the surface of the UV-curable resin 3.
The mold-release process (G) is for exfoliating the UV-curable resin 3, which has been cured by the radiation of ionizing radiation 7, from the mold 2 jointly with the base plate 4. The direction of exfoliation is based upon the following method. Namely, as illustrated in FIG. 2A, in the Fresnel-lens-configuration imparted surface of the mold 2, the lens formation grooves are formed as acute concavities/convexities. Therefore, when simply attempting to grip one side or one corner of the base plate 4 and to exfoliate the base plate 4 towards the opposite side, as illustrated in FIG. 2B the exfoliation goes beyond the center of the Fresnel lens and proceeds towards the opposite side. And the concavities/convexities of the Fresnel lens that are formed in the UV-curable resin 3 are caught and damaged. Resultantly, the Fresnel lens becomes likely to have a degraded performance as a lens. The reference symbol 16 represents the damaged portions of the lens. Therefore, the exfoliation of the lens sheet 1 from the mold 2 is done in the way the exfoliation goes on from the peripheral part towards the center portion.
This mold-release process (G) is executed in accordance with the following procedure in view of the knowledge that has been mentioned above.
As illustrated in FIG. 3, first, in a state where a central part 4a of the base plate 4 is pressed against the mold 2, a pair of diametric portions 4b, 4d are gripped and the base plate 4 is thereby lifted upward from the mold 2. A pair of the diametric portions 4b, 4d are simultaneously or alternately lifted up. As a result of this, from these diametric portions 4b, 4d and the neighborhood towards the center of the lens, the UV-curable resin 3 is exfoliated from the upper surface of the mold 2. Next, after the base plate 4 in the neighborhoods of the diametric portions 4b, 4d is once lowered onto the mold 2, another pair of diametric portions 4c, 4e are gripped and the base plate 4 is lifted upward from the mold 2. This second pair of the diametric portions 4c, 4e are also simultaneously or alternately lifted up. As a result of this, from these diametric portions 4c, 4e and the neighborhood towards the center of the lens, the UV-curable resin 3 is exfoliated from the upper surface of the mold 2. At the final stage, in a state where the central part 4a of the base plate 4 is pressed downward, all of the diametric portions 4b, 4c, 4d, and 4e are gripped and are thereby lifted up jointly and simultaneously with the pressing of the central part 4a. Thereby, the UV-curable resin 3 is completely exfoliated from the mold 2.
The lens sheet 1 that has been finished through the above-described processes is in the shape wherein the UV-curable resin layer 3 is bonded to the base plate 4.
In the projection screen, the self-sustenance of the lens is ensured through the mechanical strength of the lens sheet. As described above, the base plate 4 that has been used for manufacturing the lens sheet 1 constructs most part of the thickness of the lens sheet 1. Therefore, it has been demanded to maintain the mechanical strength of the lens sheet per se through the use of that portion.
By the way, as the projection screen goes on becoming large-sized, there has been a demand to reduce the weight, to save the resource materials, etc. of the lens sheet 1 per se and the base plate 4 and hence to make small the thickness thereof while making the area thereof large. Concretely, while the thickness of the base plate 4 that corresponds to a large-sized screen of 40 to 80 inches was conventionally to an extent of 3 mm or so, nowadays it has been demanded to make it a thickness of 1 mm or so. Ordinarily, as the method for, even when making that thickness small in that way, ensuring the self-sustenance of the lens sheet 1, it is considered as being advisable to increase the rigidity of the material of the base plate.
However, there is the problem that when increasing the rigidity of the material that material conversely becomes fragile and likely to crack. Namely, since in the above-described mold-release process (G) the base plate 4 receives a great magnitude of stress, the fragile material becomes likely to crack although it is hard. Correspondingly to this, when manufacturing the base plate with the use of a material that is unlikely to crack, the rigidity of that material decreases. Resultantly, the self-sustenance is impaired. There was therefore the problem of the so-called xe2x80x9cantinomyxe2x80x9d.
Thereupon, the present invention has an object to provide a base plate for use for a lens sheet that can realize the unlikeliness to crack while ensuring the self-sustenance, a lens sheet that uses that base plate, and a projection screen that is equipped with that lens sheet.
Hereinafter, the present invention will be explained.
In one aspect of the present invention, the above-described problems are solved by abase plate, the base plate constructing a lens sheet as a base sheet for a UV-curable resin layer by being bonded to the UV-curable resin layer and being made of the ductile material, wherein the breaking flexure by bending of the ductile material is 0.08 or more; and the Izod impact value thereof is 5 KJ/m2 or more. Also, in another aspect of the present invention equipped with the above-described aspect, the above-described problems are solved by a lens sheet comprising the above-described base plate as well as a projection screen comprising the lens sheet that is described above. Here, the xe2x80x9cductile materialxe2x80x9d is referred to as a material having a synthetic resin material having mixed therein a prescribed amount of rubber quality of material such as butadiene, including, for example, xe2x80x9cHTxe2x80x9d (impact resistance methacrylic resin) and xe2x80x9cMBSxe2x80x9d (methacrylate/butadiene/styrene copolymer resin).
If such is done as such, even when using the ductile material as the material of the base plate, it is possible to realize the unlikeliness to crack while ensuring the self-sustenance of the lens.
In the above-described aspect, the thickness of the base plate may be 1 mm or less; and the bending modulus of elasticity of the material of the base plate may be 2000 MPa or more.
If such is done as such, even when making the thickness of the base plate constructed of the ductile material 1 mm or less, it is possible to realize the unlikeliness to crack while ensuring the self-sustenance of the lens.
In a third aspect of the present invention, the above-described problems are solved by a base plate, the base plate constructing a lens sheet as a base sheet for a UV-curable resin layer by being bonded to the UV-curable resin layer and being made of fragile materials, wherein, when it is assumed that F (MPa) represents the shearing force of the UV-curable resin; h (m) represents the thickness of the base plate; E (MPa) represents the bending modulus of elasticity of the fragile material; an xcfx89 (dimensionless quantity) represents the breaking flexure by bending, the relationship of F/hExcfx89 less than 1.5 holds true. Also, in other aspects of the present invention equipped with that aspect, the above-described problems are solved by a lens sheet comprising the above-described base plate as well as a projection screen comprising the lens sheet that is described above. Here, the xe2x80x9cfragile materialxe2x80x9d is referred to as a material the Izod impact value of that is below 3.5 kJ/m2, such as, for example, xe2x80x9cPSxe2x80x9d (general use polystyrene resin), xe2x80x9cPMMAxe2x80x9d (general use polymethylmethacrylateresin), and xe2x80x9cMSxe2x80x9d (styrene/methacrylate/methyl copolymer resin).
If such is done as such, even when constructing the base plate by the use of the fragile material, it is possible to realize the unlikeliness to crack while ensuring the self-sustenance of the lens.
In the above-described aspect, the thickness of the base plate may be 1 mm or less; and the bending modulus of elasticity of the material of the base plate may be 2000 MPa or more.
If such is done as such, even when making the thickness of the base plate constructed of the fragile material 1 mm or less, it is possible to realize the unlikeliness to crack while ensuring the self-sustenance of the lens.
The above-described functions and advantages of the present invention will become apparent from the embodiments that will be explained next.